This invention relates generally to thin film coating deposition devices. More particularly, the present invention relates to shielded rotary cathodes for use in high-powered ion sputtering magnetrons.
Rotary or rotating cylindrical cathodes were developed to overcome some of the problems associated with planar magnetrons. Examples of the rotating cathode are further described in U.S. Pat. Nos. 4,356,073 and 4,422,916, the entire disclosures of which are hereby incorporated by reference. Various mounting, sealing and driving arrangements for cylindrical cathodes are described in U.S. Pat. Nos. 4,443,318; 4,445,997; 4,466,877, the entire disclosures of which are hereby incorporated by reference. Those patents describe rotating cathodes mounted horizontally in a coating chamber supported at both ends. It is often preferable to support the rotary cathode at only one end by a cantilever mount such as described in U.S. Pat. No. 5,200,049, the disclosure of which is also hereby incorporated by reference.
In recent years, the sputter coating industry has moved toward high-power sputtering. Manufacturers of such devices have been providing higher powers to the sputtering equipment to provide the end-user with increasing rates of coating material sputtered from the cathodes ultimately to increase plant productivity. With these advances have come the important problems of equipment failure due to magnetic inductive heating of parts. Manufacturing plant line shutdowns caused by such failure are extremely expensive because significant downtime and repair costs are required to fix damaged equipment. Ion sputtering magnetrons utilizing high-power alternating current are susceptible to such damage and failure from magnetic inductive heating of its sensitive parts.
For example, a rotary cathode used in an ion sputtering magnetron is susceptible to seizure from a number of failure modes. As alternating current and frequency increase, parts in the sputtering magnetron become more susceptible to heat damage. Rotation stoppage of the rotary cathode can be due to bearing seizure either in the main bearings or the rotary seal bearings. Failure can also be due to rotary seal leakage caused by overheating. Still another failure can be insulation breakdown due to exposure to overheated neighboring parts. Inductive heating is greatly magnified in ferro-magnetic materials that make up most bearings and the primary parts of the preferred rotary seal, namely, the ferrous fluid seal. Consequently, another significant failure point is the rotary seal which is susceptible to being easily damaged from excessive inductive heating. Additional failure modes with this rotary seal include seizure and atmospheric leakage which will shut down the sputtering process and, consequently, the manufacturing line, at great cost.
Another significant problem encountered is when the target material of a rotary cathode sputters mostly at one end of the target at the point where electricity from the drive shaft connects to the target. This causes non-uniform coatings on the product that need to be compensated for by masking or other problematic or expensive means. Shutting down the manufacturing line to replace those rotary cathode targets is also very costly.
Still another problem caused by high power is resistive heating. Resistive heating of parts in the current path also limits the power that can be applied.
Yet another problem is shorting and arcing at higher powers and voltages due to conductive dust from the electrical brushes that bridges insulators inside existing cathode design.
Thus, there is a need in the art for providing a high-powered ion sputtering magnetron which is less susceptible to heat damage caused by magnetic inductive heating to increase plant productivity.